1. Field of the Invention
The invention generally relates to a knocking control system and method for an internal combustion engine running on multiple fuels, and more particularly, relates to the knocking control system or method for an internal combustion engine running on multiple fuels having a different octane rating and supplied at a desired ratio.
2. Description of the Related Art
Known in the art is a knocking control system which prevents or stops a knocking in an internal combustion engine during, for example, an increased load operation. The knocking control system uses a knock sensor or an in-cylinder pressure sensor embedded in the cylinder block of the internal combustion engine to detect the amplitude of the engine vibration having a frequency specific to a knocking of the engine. When a knocking is detected, the knocking control system retards the ignition timing in accordance with the detected amplitude, i.e., the intensity of the knocking, so as to prevent or stop it.
Also, Japanese Laid-opened Patent Application No. 2001-50070 recites an internal combustion engine having a fuel supply system capable of supplying two or more different fuels, such as for example high octane gasoline and low-octane gasoline, at a desired ratio. This fuel supply ratio is changed depending on particular conditions while the engine is running so that the octane rating of the entire fuel supplied to the engine changes accordingly. With this system, for example, it is possible to prevent or stop a knocking of the engine by increasing the quantity of high octane gasoline under an engine operating state typically causing a knocking.
Also, another control system executing a similar fuel control has been shown in Japanese Laid-opened Patent Application No. 2003-120386. The control system supplies an engine with multiple fuels each having a different calorific value at a desired ratio, and when a knocking occurs, it suppresses the knocking by adjusting either the fuel supply ratio or the ignition timing appropriately.
Although JP-A-2003-120386 recites changing one of the fuel supply ratio and the ignition timing to suppress a knocking, it shows no description regarding a criteria for selection between changing the fuel supply ratio and changing the ignition timing.
Meanwhile, in a multiple-fuel engine as mentioned above, each fuel may either be supplied from a separate fuel tank which is provided in the vehicle and filled up from the outside, or produced by separating ordinary fuel into two or more fuels having a different property (e.g., octane rating) by means of a separating device provided in the vehicle. However, it is to be understood that each fuel is differently consumed and the quantity balance between the fuels is easily lost in many cases.
If fuels are supplied from the respective fuel tanks which are filled up from the outside, the aforementioned unbalanced fuel consumption may result in, for example, one of the tanks being emptied while much fuel is left in the other. In this case, it will be necessary to fill the empty tank despite the fact that there is much fuel left in the vehicle, making the refueling of the vehicle complex and burdensome.
On the other hand, when the fuels are produced by separating ordinary fuel using the in-vehicle separating device, production of the fuels continues as long as the device is running, and therefore, if the fuels are consumed unevenly, it may cause a problem that the less consumed fuel rapidly increases and fills up its tank, stopping the operation of the in-vehicle separating device.
To prevent such a problem, when an unbalanced consumption of the fuels occurs, it is necessary to equalize the remaining quantity of each fuel by increasing the consumption of one of the fuels which is larger in amount than the other.
Thus, JP-A-2003-120386 only recites changing one of the fuel supply ratio and the ignition timing to prevent a knocking, but neither shows a criteria for selection between said ratio and timing nor proposes balancing the consumption of each fuel.